Why is Steven Sinofsky out at Microsoft? Depends on who you ask.

A high-profile executive, known for being demanding and difficult to get along with, abruptly leaves one of the biggest technology companies in the world after delivering a project crucial to the business’ future.

In the past two weeks, this has happened twice.

On Oct. 29, Scott Forstall was fired from Apple. He’d been in charge of development of iOS, Apple’s mobile operating system, a critical part of the company’s present and future. Forstall, who was a good friend of the late Steve Jobs, reportedly was a contentious manager who sought to consolidate power, and his inability to get along with other executives apparently cost him his job. Forstall had just delivered iOS 6, which included the flawed Maps application that has caused Apple such grief, and he reportedly refused to sign a public apology letter.

And Monday night, Microsoft’s Steven Sinofsky abruptly signed out. Sinofsky was the executive who brought a badly needed overhaul to Office, then rescued Windows from the debacle that was Windows Vista. He oversaw the transformation of that operating system into one that tries to integrate the desktop and tablet worlds in Windows 8.

And now he’s history. Taking his place will be two veteran Windows executives: Julie Larson-Green will oversee software and hardware engineering for the OS, while Tami Reller will take charge of the business side of the house. Splitting duties in this way is not unusual at Microsoft, which at one point had three people sitting in its Office of the President.

On one level, this comes as a huge surprise. Sinofsky was seen as the heir apparent to CEO Steve Ballmer, a competent, smart and driven executive who has delivered two crucial upgrades to Windows on time. With Windows 8, he’s laid a foundation for Microsoft’s future, with an attempt to unify its interface across mobile, desktop and gaming platforms. Sinofsky has overseen a controlled revolution for the company, and while reviews of Windows 8 are mixed and it’s not yet clear whether this huge bet will pay off, Sinofsky has gotten lots of credit for the effort.

So why is he suddenly sitting at home, exploring other options? That depends on who you ask.

Critically, Sinofsky was not ousted because of any issues with the launch of Windows 8 or the Surface, sources tellus; in fact, it’s possible that his departure was already planned, but his ability to execute on Windows 8’s retail release was seen as an asset worth keeping him around long enough to see it through. But his attitude (and skill set) as an aggressive, tightly-siloed Windows boss — not a holistic Microsoft boss — may have done him in. Given that the future of Microsoft’s ecosystem would require tight collaboration between disparate divisions, Sinofsky’s future path as an executive at Microsoft was essentially at an end.

Bohn says Sinofsky also was responsible for the departure of many talented people at Microsoft. For example, Sinofsky was reportedly behind killing of the Courier project, a dual-screen tablet device. That action led to the departure of Xbox guru J Allard.

Indeed, Sinofsky was known to be rude and belittling even to non-Microsoft employees. There’s this now-infamous anecdote from the launch of the Surface tablet:

Microsoft executives, however, were largely mum on how Surface would affect the company’s relationships with PC makers, the hardware companies that are the vehicles for sales of Windows software. With its new tablet, Microsoft will effectively be competing directly with its biggest customers.

When asked whether Surface would damage those ties, Steven Sinofsky, the president of Microsoft’s Windows division, gently pushed a reporter in the direction of a stand of Surface tablets and said, “Go learn something.”

In an email to Microsoft employees, Sinofsky said his decision to leave was personal. He wanted to reflect and “seek new opportunities.” And he advised everyone to ignore all these rumors about why he’s leaving:

Some might notice a bit of chatter speculating about this decision or timing. I can assure you that none could be true as this was a personal and private choice that in no way reflects any speculation or theories one might read — about me, opportunity, the company or its leadership.

As I’ve always believed in making space for new leaders as quickly as possible, this announcement is effective immediately and I will assist however needed with the transition.

Corporate life is complex, and it’s likely the truth is a combination of all three explanations. But despite being an ambitious jerk, Sinofsky was a man with a vision about what personal computing can be. That had been badly needed at Microsoft, and the company will miss that vision as it embarks down the path carved out by Windows 8.